Summary The Voyageur Airlines de Havilland DHC-7 (VAL712) departed Masset, British Columbia, at about 1230 Pacific daylight time en route to Vancouver at 17000feet. A Cessna 421 (C-GKOS) departed Port Hardy at 1330 en route to Red Deer, Alberta. C-GKOS climbed eastbound initially to 15000feet and was subsequently cleared to maintain 17000feet. The two aircraft tracks converged near the KELSY intersection. Both flights were radar-identified in controlled airspace, flying in accordance with instrument flight rules, and provided air traffic control services by the Nootka radar controller in the Vancouver Area Control Centre (ACC). At about 1351, as C-GKOS approached the KELSY intersection, the Nootka radar controller verbally handed off the Cessna 421 to the Comox terminal controller. The Comox controller identified the handoff target but also questioned the proximity of another aircraft target, VAL712. The Nootka radar controller recognized the traffic conflict and instructed C-GKOS to maintain 15000feet. He then received a radio call from VAL712 about the proximity of C-GKOS. By then, the two aircraft had passed each other and were on diverging tracks. The two aircraft came within 0.8nauticalmile (nm) of each other at 17000feet. Visual meteorological conditions existed at the time. Ce rapport est galement disponible en franais. Other Factual Information The KELSY intersection is a reporting point on V347 at the border of the Vancouver civilian airspace and the Comox military airspace, 51nm east of Port Hardy, British Columbia. Figure1. Relative flight paths of C-GKOS and VAL712 At 1351:50 Pacific daylight time,1 when VAL712 and C-GKOS were about 1.7nm apart at 17000feet, the Nootka radar controller (the radar controller), prompted by the Comox controller, recognized the imminent risk of collision. At 1352:05 and again at 1352:17, the radar controller tried to instruct C-GKOS to descend to 15000feet. However, he twice used the call sign GKS rather than GKOS, and the pilot of C-GKOS did not respond to those instructions. At 1352:21, he used KOS, and the pilot immediately acknowledged the instruction to descend. The radar controller did not advise either aircraft of the other. Radar data show that C-GKOS began to descend from 17000feet about 40seconds after the first transmission to descend. During his attempted transmissions to C-GKOS to descend to 15000feet, the radar controller did not convey a sense of urgency to the pilot, nor did he incorporate the standard published safety alert phraseology2 to indicate a need to commence an immediate descent. At 1352:40, the VAL712 pilot advised the radar controller that he had received a traffic alert from the on-board traffic alert and collision-avoidance system (TCAS) triggered by C-GKOS's crossing ahead of them; the VAL712 pilot had C-GKOS in sight. C-GKOS began to descend after these communications. Air traffic control radar data show that the two aircraft were on a collision course of constant relative bearing until 10seconds before the Comox controller advised the radar controller about the proximity of VAL712. At this point, the collision geometry began to change as C-GKOS increased its speed during normal climbout profile acceleration. At the time of the incident, the workload for the Nootka positions (radar and data) in the West Complex of the Vancouver ACC was moderate, with normal complexity. The West Complex would normally have been staffed by seven controllers and one supervisor. At the time, the unit was staffed with eight controllers and no supervisor. Only six controllers were actually at their positions, however; the other two were on scheduled break. The Nootka sector was combined with the Holberg sector, and together they had a dedicated radar controller and a dedicated data controller. Given the traffic volume and complexity at the time, it was not unusual to combine the sectors. In the 25 minutes before this incident, the radar controller had been in radio contact with 21aircraft: 13high-level aircraft offered no conflict; 5low-level aircraft required action by him to ensure separation was maintained; and 3low-level aircraft offered no conflict. The radar controller made about 45 radio transmissions during this period: only 11 were of a controlling nature; the rest were simple acknowledgements or frequency changes. Appendix A summarizes the chronology of main events for the 20minutes preceding the incident. In the 6 minutes between the radar controller's clearing of C-GKOS to maintain 15000feet (1335:09) and the subsequent clearance to 17000feet (1341:24), 3radio acknowledgements, 3handoffs, and one period of 3.5minutes of uninterrupted silence occurred. During this time, C-GKOS was the only aircraft changing altitude. In the 5minutes before the Comox controller pointed out the conflict with VAL712 (1351:42), the radar controller was actively involved with managing N199BB's departure and climbout of Port Hardy, PCO807's arrival and setup for an approach to Port Hardy, and C-GKOS's climb en route. In the event of an increase in traffic volume and complexity, a controller in this complex has the option of splitting his or her sector to reduce the workload for that position. Such a split is commonplace and typically involves engaging a controller to open up another position to handle a specific area of responsibility. Splitting a sector is usually coordinated with the unit supervisor or the ACC shift manager, but if neither is available, a senior controller can initiate and coordinate such a split. In this incident, the involved radar controller assessed that the workload at the time did not warrant a sector split. NAV Canada instructions stipulate that the radar and the data positions are both responsible for continuously scanning the flight data board for conflicts.5 After the radar and data positions have coordinated, the radar controller is responsible for maintaining separation between radar-identified aircraft. The flight progress strips for all the aircraft had been correctly prepared and arranged on the flight data board in accordance with normal unit practices. The radar controller had set his radar information monitor to the usual radius range of 200 nm, and the aircraft targets and data blocks (tags) were correctly displayed. This 200-nm radius range ensures that the entire sector airspace was displayed. Because of the number of aircraft targets and tags, some of the data blocks intermittently overlapped each other. Neither the data controller nor the radar controller placed a warning indication on the strips of C-GKOS or VAL712 to indicate the potential conflict, even though both aircraft would be flying at 17000feet. The radar controller's initial assessment, made when he cleared C-GKOS to 17000feet, was that the two aircraft would not conflict when their flight paths crossed. He did not use any of the display tools, such as predicted track line or range bearing line, to determine an accurate track crossing time for the two aircraft. No estimates were calculated for the point where the two aircraft crossed tracks.